The overall objective of this investigation is to obtain electrophysiological and pharmacological data that will lead to a better understanding of the role of the basal ganglia in motor function. We have decided to concentrate on electrophysiological and pharmacological investigations of the synaptic mechanisms and synaptic transmitters associated with the major afferent and efferent pathways of the globus pallidus (GP). The GP receives input directly or indirectly from all other basal ganglia nuclei and relays this information primarily to the thalamus to eventually influence motor activity in the corticospinal system. Most of the electrophysiological investigations of the pallidal system have been conducted using cats and there have been serious problems associated with electrophysiological studies on this system in cats: 1) The entopeduncular nucleus (feline equivalent of the primate medial pallidal segment) is located within the internal capsule punctuated by numerous low threshold capsular fibers. 2) Electrophysiological studies have been conducted on the pallidothalamic projection system following stimulation of a structure labelled ansa lenticularis in most cat atlases: but recent anatomical studies have shown that this is a misidentification and this structure is not equivalent to the ansa lenticularis of primates and it does not originate from GP. Experiments on the pallidothalamic and striopallidal pathways have provided contradictory results because of these and other problems. There is almost no information available on the GP reciprocal synaptic connections with the subthalamic nucleus (STN). Only the striopallidal system has been studied pharmacologically. We plan to use Macaca mulatta monkeys as our experimental animal and will employ intracellular and extracellular microelectrode techniques to explore the synaptic mechanisms and synaptic transmitters involved in the following pallidal pathways: 1) pallidothalamic, 2) pallidosubthalamic, 3) striopallidal, and 4) subthalamopallidal. Synaptic mechanisms will be defined in terms of monosynaptic and/or polysynaptic EPSPs and IPSPs when possible; microiontophoretic techniques will be employed to pharmacologically characterize the putative neurotransmitters in these pathways.